Various purine derivatives are known including 9-deazaguanines such as 8-desamino-9-deazaguanines and their derivatives having activity as inhibitors of purine nucleoside phosphorylase (PNP-4). For example, see U.S. Pat. No. 4,923,872 and related patents, and the patent application W09106-548A and W09010-631A as well as U.S. Pat. Nos. 5,008,270; 5,008,265; 4,985,434; and 4,985,433. These are incorporated by reference to show related references as cited in each.
The previous disclosures differ from the present invention of the Formula I at least by the 8 halo or 8-hydroxy substituent now found to provide PNP inhibitor activity.